Re: [PATCH v2 09/13] x86/emulator: Refactor FXSAVE_AREA to use wrappers

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.11.2024 15:33, Alejandro Vallejo wrote:
> --- a/xen/arch/x86/x86_emulate/blk.c
> +++ b/xen/arch/x86/x86_emulate/blk.c
> @@ -11,9 +11,12 @@
>      !defined(X86EMUL_NO_SIMD)
>  # ifdef __XEN__
>  #  include <asm/xstate.h>
> -#  define FXSAVE_AREA ((void *)&current->arch.xsave_area->fpu_sse)
> +/* has a fastpath for `current`, so there's no actual map */
> +#  define FXSAVE_AREA ((void *)VCPU_MAP_XSAVE_AREA(current))
> +#  define UNMAP_FXSAVE_AREA(x) VCPU_UNMAP_XSAVE_AREA(currt ent, x)

The typo of the first argument strongly suggests that the macro should
already now evaluate its parameters, also pleasing Misra.

>  # else
>  #  define FXSAVE_AREA get_fpu_save_area()
> +#  define UNMAP_FXSAVE_AREA(x) ((void)x)

If only for consistency and to avoid setting bad precedents - parentheses
please around x.

> @@ -292,6 +295,9 @@ int x86_emul_blk(
>          }
>          else
>              asm volatile ( "fxrstor %0" :: "m" (*fxsr) );
> +
> +        UNMAP_FXSAVE_AREA(fxsr);
> +
>          break;
>      }
>  
> @@ -320,6 +326,9 @@ int x86_emul_blk(
>  
>          if ( fxsr != ptr ) /* i.e. s->op_bytes < sizeof(*fxsr) */
>              memcpy(ptr, fxsr, s->op_bytes);
> +
> +        UNMAP_FXSAVE_AREA(fxsr);
> +
>          break;
>      }

So for now the emulator only supports FXSAVE / FXRSTOR. That'll need to change
sooner or later. Is it really appropriate in that light to name the new macro
after FXSAVE, when the underlying machinery uses all XSAVE?

Jan